That wasn't Traviss. She was just following the original Marvel Comics that had Mandalore being low tech.

Kegg wrote:

And that's still canon because the EU decided that maybe the stormtroopers aren't all clonetroopers because that makes handling the canon a lot easier as no pre-AOTC works suggested they were an army of clones.

That is not true actually. The idea of them being clones was suggested in 1981 in the Star Wars Compendium 2.